1. Field of the Invention
The present invention relates to methods and apparatus for monitoring and/or controlling therapeutic beds and mattress systems and the patients supported thereon. More particularly, the invention relates to monitoring angular deviations of the mattress surface and patient from the flat, horizontal position and for controlling the system in response.
2. Description of Background Art
Therapeutic supports for bedridden patients have been well known for many years. Well known therapeutic supports include (without limitation) low air loss beds, lateral rotation beds and fluidized bead beds. Commercial examples are the "KinAir", "RotoRest" and "FluidAir" beds, all of which are products manufactured and commercialized by Kinetic Concepts, Inc. of San Antonio, Tex. Similar beds are described in U.S. Pat. Nos. 4,763,463, 4,175,550 and 4,635,564, respectively.
Other examples of well-known therapeutic supports for bedridden patients are the inflatable mattresses, mattress overlays or mattress replacements that are commercialized independent of a rigid frame. Because of the simpler construction of these products separate from a costly rigid frame, they tend to be more versatile and economical, thereby increasing options for customers and allowing them to control costs. A specific example of one such mattress is the "TheraKair" mattress, described in U.S. Pat. No. 5,267,364, dated Dec. 7, 1993, also manufactured and commercialized by Kinetic Concepts, Inc. The TheraKair mattress is a composite mattress including a plurality of transversely-oriented inflatable support cushions that are controlled to pulsate and to be selectively adjustable in groups.
Most therapeutic mattresses are designed to reduce "interface pressures", which are the pressures encountered between the mattress and the skin of a patient lying on the mattress. It is well known that interface pressures can significantly affect the well-being of immobile patients in that higher interface pressures can reduce local blood circulation, tending to cause bed sores and other complications. With inflatable mattresses, such interface pressures depend (in part) on the air pressure within the inflatable support cushions. Although a number of factors are at play, as the cushion's air pressure decreases, the patient interface pressure also tends to decrease, thereby reducing the likelihood that the patient will develop bedsores and other related complications. Hence the long-felt need to have an inflatable mattress which optimally minimizes the air pressure in the inflated cushions.
The desired air pressure within a given cushion or group of cushions may also depend on inclination of the patient support, or portions thereof. For instance, it is known that when the head end of a bed is raised, a greater proportion of the patient's weight tends to be concentrated on the buttocks section of the mattress. Hence, it has long been known to divide inflatable therapeutic mattresses into groups of transversely-oriented inflatable cushions corresponding to different regions of patient's body, with the pressure in each group being separately controlled. Then, when a patient or attendant controls the bed to elevate the patient's head, pressure in the buttocks cushions is automatically increased to compensate for the greater weight concentration and to prevent bottoming of the patient. ("Bottoming" refers to any state where the upper surface of any given cushion is depressed to a point that it contacts the lower surface, thereby markedly increasing the interface pressure where the two surfaces contact each other.)
It is also well known in the field of treating and preventing bedsores, that therapeutic benefits may be obtained by raising and lowering (or "pulsating") the air within various support cushions. The effectiveness of this therapy may be reduced or negated if the surface inclination of a region (i.e., angle of the region relative to a horizontal plane) changes, or if the pressure in the appropriate support cushions is not properly adjusted. As with bottoming, such a condition may occur when the head of the patient is raised to facilitate, for example, feeding of the patient. As the angle of the head end of the support mattress (and thus the angle of patient's head) becomes greater, the patient's weight redistributes. Consequently, a greater proportion of the patient's weight is concentrated on the patient's buttocks region, while less weight is concentrated on the head and back region.
It is also known to subject patients to gentle side-to-side rotation for the treatment and prevention of pulmonary problems. It is known to achieve such rotation therapy by alternating pressure in two inflatable bladders which are disposed longitudinally under the support mattress along the length of the left and right sides of the patient. Consequently, as one of the inflatable bladders inflates, the patient rotates by an angle up to approximately 45 degrees. Although references such as RWM's U.S. Pat. No. 4,769,584 have long taught the importance of sensing the actual angle of rotation, the actual rotation angle in inflatable supports was typically controlled by the amount of pressure applied to the pivot bladder without measuring the actual angle of rotation attained. Unfortunately, during this treatment, if too great of a rotation angle is achieved, then the patient tends to roll to the edge of the support mattress as one of the inflatable bladders inflates. Therefore, if an apparatus could be designed which would measure and control rotation angles of the therapeutic bed surface this would prevent attaining excess angles resulting in the patient rolling to the edge of the support mattress during side-to-side alteration, and possibly falling off the support mattress. Also, if a minimum rotation angle of about twenty five degrees is not attained, then minimal or no therapeutic value is received by the patient.
It has also long been known in the art to control other aspects of the patient surface in response to inclination of specific portions of the patient. For instance, the Eggerton "Tilt and Turn" bed popular in the 1980's was adapted to raise a restraining portion of the patient surface during lateral turning, in order to help prevent the patient from rolling off the bed. Another example is the automatic knee gatch feature popularized in Hill-Rom frames, particularly such as described in U.S. Pat. No. 3,237,212. Such knee gatch feature was adapted to automatically raise the knee section of the patient support whenever the patient or caregiver desired to raise the head section, hence compensating to prevent a patient from sliding toward the foot end of the bed when the head section was raised.
The concept of controlling air pressure inflatable support cushions in response to changes in the patient surface is at least plausible in bed systems which utilize a rigid frame structure beneath the patient. The frame structure provides an attractive location for mounting the transducers required for such control. With flexible mattresses, to position any foreign devices in closer proximity to a patient, because a patient might be injured by contact with the device would be steadfastly avoided, mounting a sensor to a rigid base board helps shield a patient from contact with the sensor. The result, though, is that a health care facility is inclined to acquire the entire bed system in order to gain the benefits of such technology--an acquisition which may not be readily affordable. Such acquisitions also limit the health care facility to using specific mattresses with specific frames, rather than separately selecting and interchanging the preferred mattresses and bed frames. Interchangeability, on the other hand, would tend to maximize the facilities cost containment and efficiency.
Unfortunately, conventional support mattresses fail to properly adjust the pressure within the support cushions as the surface angles of the support mattress vary. Therefore, if an apparatus could be implemented which would adjust the pressure within the support cushions as the mattresses surface angles change, the pressure points on the patient would be significantly reduced, thereby preventing or significantly reducing the number of bedsores.
Others have taught that the desired air pressure within the air cushions may depend in part on the angle to which the patient is desired to be rotated. For instance, U.S. Pat. No. 5,003,654 dated Apr. 2, 1991 described an oscillating low air loss bed which laterally rotates a patient to varying degrees depending in part on the pressure within the cushions which achieve the turn.